The present invention relates to a power steering system.
Typically, in the state of steering maintained after performing assist for steering, the power steering system carries out control for decreasing the rotational speed of an electric motor so as not to increase the hydraulic pressure within an apply-side pressure chamber. Then, since a closed circuit connecting a reversible-type oil pump to the apply-side pressure chamber is maintained at the high pressure, the oil pump produces great surging. In addition to surging, the electric motor and the oil pump also produce dynamic friction. With this, in some instances, the electric motor cannot maintain its rotation speed to repeatedly carry out rotation and stop until subsequent assist for steering is performed, providing disagreeable feel to a driver.
In order to cope with this problem, there is a power steering system wherein a branch passage is arranged to convey part of discharged oil of the oil pump to the outside of the two pressure chambers in a branched way. Specifically, discharged oil of the oil pump flows to the outside of a hydraulic power cylinder through the branch passage, reducing surging of the oil pump in the state of steering maintained after performing assist for steering, thus achieving restraint of pump stop.